Evaluating the biotic integrity of watersheds in the Sierra Nevada, California

We developed a watershed index of biotic integrity that used whole watershe d variables for metrics rather than site-specific variables. We used the in dex to evaluate the biological health of 100 watersheds in the Sierra Nevad a of California. The inner scores, which were based on various measures of distribution and abundance of native fish and frogs, indicated that 7 of th e watersheds were in excellent condition (high biotic health), 36 were in g ood to very good condition 48 were in fair condition, and 9 were in poor co ndition. The biggest factors contributing to low index scores were large da ms and introduced fishes, although measures of road density and indicators of intensity of use of terrestrial habitats were also important. Large area s of the Sierra Nevada that were once fishless now contain trout in most wa ters, anadromous fishes are excluded from many streams from which they were once abundant assemblages of native fishes have been disrupted, and ranid frogs have been extirpated from many areas All watersheds in the Sierra Nev ada have thus experienced loss of biotic integrity, but some have suffered much less than others Evaluations of the biotic integrity of watersheds ove r wide regions can help managers set priorities for watershed-oriented syst ems of aquatic conservation and provide starting places for more-intensive studies.